Cleavage of Parathyroid Hormone to the 1-34 and 35-84 Fragments by Cathepsin D-Like Activity in Bovine Parathyroid Gland Extracts

We have obtained a crude enzyme preparation from bovine parathyroid gland homogenates which when incubated with PTH, cleaves the hormone into two major fragments. Isolation and chemical analysis has led to the identification of these peptides, the 1-34 fragment and the 35-84 fragment. Digestion of PTH was totally inhibited by the inclusion of the cathepsin D inhibitor, pepstatin, in the enzyme digest. A comparison of the digest obtained using the crude enzyme fraction vs. digestion of PTH by purified bovine cathepsin D led to the findings that the same peptide products were formed in each case. The natural 1-34 hormone fragment derived from the procedure has been determined to be fully biologically active in a bone resorption system.